I have discovered a better way of operating an annular, disk-shaped attrition zone for working slurried material in pulpers and refiners. The turning rotor bars that confront stator bars in such attrition zones centrifugally pump the slurry radially outward from the inside to the outside of the attrition zone as the bar crossings work the material flowing through.
Such centrifugally pumping, annular attrition zones experience many problems. In pulpers, they need a cleaner to keep large clumps of fiber from plugging the inside entrance to the attrition zone, and cleaners find it difficult to exclude contaminants and overly large fiber clumps while admitting suitable slurry to the attrition zone. The pumping force of the attrition zone, especially when combined with a restrictive cleaning bonnet, creates a high vacuum under the rotor. Resisting the substantial force of this vacuum requires a strong rotor, a large thrust bearing, an elaborate packing gland around the rotor shaft, and a sturdy mechanism for moving the rotor axially to adjust the bar clearance gap in the attrition zone.